The Norovirus infection made Christmas and New Year very unpleasant for over 150,000 people. They were unlucky enough to spend the holiday period with vomiting and diarrhoea, and in some cases stomach pains and a temperature. Numbers of cases now seem to be declining, but this is no cause for complacency. We should all keep taking precautions.

This is a highly infectious disease caused by a virulent virus that changes from year to year. Any immunity people gained from having the infection in the past subsides as each new variant comes along. Last autumn was a particularly bad time, with schools, hospitals and workplaces needing to close for short – but disruptive – periods of time. The Health Protection Agency estimated that more than a million of us have had it during the current outbreak.

Fortunately, most people recover within 2 or 3 days. But anyone who doesn’t will need professional advice, as will frail elderly people, young children, people with chronic diseases and pregnant women. These need to make sure they stay well hydrated by drinking plenty of fluids.

It’s a mammoth task to clean thoroughly all potential contaminated surfaces as the Norovirus can survive for up to 5 days. It’s not just public lavatories and the like that need attention; surfaces on public transport can become contaminated many times in a day.

The Norovirus is probably the World’s commonest cause of gastroenteritis (stomach bug), and its spread and variants are under worldwide surveillance. So far there is neither a medicine to deal with it nor immunisation against it.

What can be done? If you catch it stay away from other people until you are better. In particular, avoid crowds or places where you can readily pass it on to others. Thorough hand-washing several times a day is important, and especially after touching anything potentially contaminated. There is debate about the value of hand disinfectants, which are probably useful in places where you cannot wash your hands. But washing with good old-fashioned soap and water for at least half a minute is still the best standby.

Although this virus may at last be on the decline, it’s still worth taking the precaution of washing your hands regularly and thoroughly – and not just because of the Norovirus. We become complacent about infections at our peril. This may have been a short-lasting one, but there are others that are more persistent or dangerous.

Hand-washing offers simple, effective protection, and the facilities are readily available. Why not use them?

It’s striking how many people have signed up at our local leisure centre in the last couple of weeks. But if this year is like previous ones, it’s likely that many will drift away again in the next month or so. Plainly, for many people leisure centres are not the answer to how to keep fit and healthy.

Perhaps January is a good time to look creatively at what we want to achieve and to find ways to increase our everyday activity levels throughout the whole year ahead. Even the simplest ideas can be effective. Finding a new place to park that bit further from work and walking the extra distance every day can make a real difference over time – and it might even save on parking fees. Deciding always to use the stairs rather than the lift is another good idea. It’s always surprising to see how many people wait for a lift to go up just one floor – and even more surprising how many take that lift back down!

Organisations can be creative too. Indeed, one major organisation has found imaginative ways to encourage its employees to use the stairs. First, they programmed lifts to stop only at alternate floors, which meant employees had to plan their lift journeys. Then they made the stairways more inviting with attractive paintwork, good lighting and soft music. People started using the stairs and these became part of the building’s social area. This wasn’t just good for the employees: overall productivity increased.

When thinking about keeping active over the year ahead, those with children – particularly adolescents – may be facing a greater challenge than just motivating themselves. Surveys are showing low levels of activity in many of today’s adolescents, with a lot of time spent watching TV or at the computer studying, networking and playing games. Unfortunately, habits tend to stick: inactive children may end up as inactive adults.

Quite how damaging inactivity can be has been highlighted in a recent interesting study in Sweden*. This followed over 1 million adolescents for 24 years; during this time there were more than 26,000 deaths. The study showed that low muscular strength in adolescence was associated with a substantially increased risk later of heart disease and mental illness.

Of course, such an association does not prove cause and effect: it is not the same as demonstrating that increasing the adolescents’ strength improves their outlook. Such a direct link would be hard to prove conclusively. But other studies, some dating back to the 1980s, have also attested to the benefits – in terms of avoiding illness and living longer – of maintaining fitness levels from adolescence through to later adult life.

January is a great month for thinking about getting active. The key is to remember the other 11 months too.

“Non-communicable diseases” are those – such as heart disease, diabetes, cancer and lung disease – which arise from lifestyle and environmental factors rather than from germs and infections. Before the 20th Century, most deaths were due to infectious diseases. Now, nearly two-thirds of deaths worldwide are due to non-communicable diseases.

Tackling this presents an enormous challenge globally. A United Nations meeting in New York in 2011 identified the four major factors that we all need to address: poor diet, physical inactivity, tobacco use and alcohol intake.

But persuading adults to change their lifestyle is far from the whole picture. There is growing evidence that we also need to focus attention on children – and even on babies before they are born!

Some of these diseases have their roots in childhood. Coronary artery disease is one that has been extensively investigated. Many of the risk factors can be shown to have their onset in childhood, when dietary and other habits begin to form under the influence of family members and childhood friends. Parents need better information on the importance of encouraging physical activity and a good diet in their children.

A recent article in The Lancet* goes further and suggests that disease in later life can be affected by what happens to us before we are born. For example, if the mother is poorly nourished or has diabetes, this is associated with her unborn child being at greater risk of developing non-communicable diseases when it reaches adulthood.

There is also some evidence that if a pregnant mother or infant is exposed to certain pollutants in the atmosphere or in food, this too may have an impact on the child in the long term, potentially affecting its immune responses and its neurological and reproductive functions when adult. How this happens probably relates to changes in the way the baby’s DNA is processed during its development, when substantial changes can be passed from cell to cell as they divide and grow. These changes can last and have a knock-on effect in adult life.

These findings add to the urgent need for worldwide action to curb environmental pollution from harmful chemicals.

Just when most of us have got it fixed in our heads that being overweight is bad for us, along comes a major scientific paper* suggesting that being somewhat overweight actually reduces our risk of dying. What’s going on?

The researchers looked systematically at around 100 previous studies that together involved 2.88 million participants (of whom around 270,000 died during the study period). Each study divided the participants up according to their Body Mass Index (BMI), putting them into the standard categories of “underweight”, “normal weight”, “overweight” and three levels of “obesity”. The studies then worked out how likely it was – compared with people in the normal weight category – that people in each of the categories would die within a given period of time (such as one year or five years). In statistics this likelihood is referred to as the “hazard ratio”.

For a long time it was thought that the normal weight people would be the least likely to die in a given period. But when the data from all the studies were pooled together, the people with the lowest risks of dying turned out to be those in the overweight category and the lowest level of obesity category!

The effect is quite a small one – it’s only about a 5% lower risk. And the risk of dying climbs steeply for the level 2 and 3 obesity categories, where it is about 30% higher than for normal weight people.

Nevertheless, this result seems surprising. It’s sometimes referred to as the “obesity paradox”. What should we make of it?

The most important point, as most scientists would agree, is not to conclude that we should all start piling on the pounds. There is strong evidence that increasing levels of body fat can lead to all sorts of potentially harmful changes in the body. Diseases such as heart disease and diabetes become more likely. These may not result in death, but they can still be disabling and unpleasant. And once you start to build up body fat, it becomes harder to get rid of, so it is wise to take action straightaway to avoid any possibility of ending up in the high-risk obese categories.

But how do scientists explain the slightly lower risk of dying among those who are overweight? So far, there is no clear explanation, although several factors may contribute.

Firstly, the measure used – the BMI – is less than ideal. It is a simple calculation of your body weight (in kilograms) divided by your height (in metres) squared. “Normal weight” is agreed internationally to be a BMI score of 18.5 to 25, while “overweight” is 25 to 30. One big problem with this is that people with a lot of muscle but not much fat – such as men who get fit through weight training – end up being classed as “overweight”, even though they are in great shape. Highly muscular sportsmen can even be classed as “obese” by this measure! Having some fit, healthy people in the overweight category could well affect the results.

Many of the studies focused on older people, and the finding is even stronger among the over-65s. Being in the overweight category makes it around 10% less likely an older person will die in a given period compared with older people in the normal weight zone. It is possible that some extra body fat could help older people survive serious illnesses.

It is quite likely there are other processes going on as well. People’s bodies may perhaps handle excess fat in different ways. Or it might be that something like fitness is ultimately a more important factor than body weight. And some of the people in the overweight category may well have been taking action to lose body fat, which has been shown to bring health benefits. There’s plenty still to explore. For example, the lower end of the normal BMI range is associated with higher mortality than the upper part. There’s no clear explanation for this.

This study has certainly raised intriguing questions. Hopefully, future research will start to answer some of the questions and provide a better indication of the dangers and benefits of body fat. Until then, though, the basic advice doesn’t change. To stay healthy and avoid future disease, watch your weight!